Treatments for diseases such as cancer, for which the ultimate therapeutic goal is to kill the diseased cell or prevent or inhibit its reproduction, include the administration of cytotoxic drugs. Cytotoxic drugs include many chemotherapeutic agents that are used in the treatment of cancers, including alkylating agents, antimetabolites, and toxins. Most cytotoxic drugs are non-selective, killing healthy cells as well as diseased cells, which contributes to undesirable side effects when these agents are delivered systemically. Thus, a need exists for cytotoxic agents that are more efficacious and more selective for diseased cells over healthy cells.